Paint formulations that are fluid as applied are often transferred to the article being coated by a spraying technique. Various types of paint spray equipment are known and used in the industry. Such equipment includes hand-held spray guns, electrostatic spray guns, turbobells, robot arm-mounted air atomizers, and the like. The transfer efficiency, that is the percentage of sprayed material that is actually transferred to an article being coated, varies from installation to installation. Transfer efficiencies of from about 10 or 20 percent, to about 80 percent or more, are not uncommon. Thus even at a relatively high transfer efficiency, such as 70 or 80 percent, a significant amount of paint formulation is oversprayed (not transferred to the article being coated).
Such paint spraying is commonly done in an enclosed area called a paint spray booth. Paint spray booths generally are comprised of a chamber, a duct system for passing air through the chamber, a sump that contains a circulating fluid located at the bottom of the chamber, and often means for pumping a portion of the sump fluid into the chamber to form a liquid curtain. The circulating fluid is generally a hydrophilic fluid. The air passing through the chamber may carry a portion of the paint formulation to the article being coating, increasing transfer efficiency and reducing the amount of overspray. Such air stream also generally captures at least a portion of the overspray, carrying it to the hydrophilic fluid. The liquid curtain likewise generally captures at least a portion of the overspray, carrying it downward to the sump.
The paint spray booth management programs of concern to the present invention are those that employ as the hydrophilic liquid an oil-in-water emulsion. Such programs are known in the industry, and descriptions of such systems can be found in U.S. Pat. No. 4,378,235 (issued Mar. 29, 1983, inventors Cosper et al.), U.S. Pat. No. 4,563,199 (issued Jan. 7, 1987, inventors Lindenberger et al.), U.S. Pat. No. 4,750,919 (issued June 14, 1988, inventors Patzelt et al.), and U.S. Pat. No. 4,919,691 (issued Apr. 24, 1990, inventors Patzelt et al.), all of which are incorporated hereinto by reference.
Such oil-in-water emulsions are highly advantageous. The paint formulations used in paint spray booths contain some amount of volatile organic carrier ("VOC"), and some VOC can evaporate into the air during the spraying operation. The oil-in-water emulsion absorbs VOC from the air, reducing potential VOC emissions. Other constituents of the paint formulation(s) being sprayed are also received by the emulsions.
It is desirable to detackify the paint solids received by the hydrophilic fluid. It is desirable to maximize the hydrophilic fluid's loading capacity for paint solids. It is desirable to minimize the deleterious effects caused by the presence of paint solids on the movement and further processing of the hydrophilic fluid. These objects have become more challenging to achieve as industry turns from low solids solution lacquers and the like, to paint formulations containing less VOC, such as high solids enamels, base coat-clear coats, two-component urethanes, and the like. Such changes as to the type of paint formulations employed reduce VOC emissions. Such changes also increase and/or exasperate the handling and removal of oversprayed paint solids.